Beamograms - Setting Parameters
Sound speed refers to speed of sound within the medium in which the recording was made, usually either air or water. The speed of sound varies in these media based on a number of parameters, including the temperature and density of the media. However, a useful approximate value for the speed of sound in air is 330 meters/second, and in saltwater a useful approximate value is 1500 meters/second.
Enter the X and Y locations in the sensor array. The sensors should have coordinates that indicate positions (in meters) relative to one another.
If you would like the signal to be bandpass filtered before the beamformer calculation, enter low and high frequency limits to define the bandwidth that will be passed through the filter.
To alter the Beamogram parameters after a beamogram has been created, choose View > Beamogram Configuration.
The Record size is the number of samples of sound over which a beam will be computed. The system then ‘hops’ by the number of samples given in Hop size and repeats the computation. This process is repeated iteratively for all beams.
If the gain imbalance between the recorded channels is large, it may become the main information used
in the beamformer computation. Therefore, unless the microphones and recording unit are carefully
calibrated to produce a uniform gain, normalizing the signal will be useful.
The Minimum bearing and Maximum bearing values (in degrees) define the range over which the series of individual beams will be calculated. It is generally useful to restrict the range to the directional region most likely to contain the source. The Number of bearings is the number of beams that will be computed. A larger number of beams will usually produce a more accurate measurement. The resolution of the beamformer system is defined by the difference between the Maximum bearing and Minimum bearing, divided by the Number of bearings.
Bearing Coordinate System
When the Reference bearing is set to zero degrees, the array is set to be perpendicular to the sound source. Altering the reference angle alters the orientation of the array to the sensor for the purposes of the beamformer calculation. The rotation of the Bearing Grid that results from altering the reference angle can be specified as either Counterclockwise or Clockwise.
You can create different subsets of channels to use with the beamformer calculation and compare the results.
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